Xylose is an abundant sugar present in lignocellulosic biomass, a renewable feedstock for producing bioderived chemicals. However, the use of lignocellulosic biomass and the production of bioderived chemicals are limited by the naturally low xylose uptake in microbial organisms. Therefore, a microbial organism that can use xylose to produce bioderived compounds, such as xylitol, represents an unmet need.
Xylitol is a five-carbon sugar alcohol widely used as a low-calorie, low-carbohydrate alternative to sugar (Drucker et al., Arch of Oral Biol. 24:965-970 (1979)). Xylitol is approximately as sweet as sucrose but has 33% fewer calories. Xylitol has been reported to not affect insulin levels of people with diabetes and individuals with hyperglycemia. The consumption of xylitol is also reportedly beneficial for dental health, reducing the incidence of caries. For example, xylitol in chewing gum is reported to inhibit growth of Streptoccocus mutans (Haresaku et al., Caries Res. 41:198-203 (2007)), and to reduce the incidence of acute middle ear infection (Azarpazhooh et al., Cochrane Database of Systematic Reviews 11:CD007095 (2011)). Moreover, xylitol has been reported to inhibit demineralization of healthy tooth enamel and to re-mineralize damaged tooth enamel (Steinberg et al., Clinical Preventive Dentistry 14:31-34 (1992); Maguire et al., British Dental J. 194:429-436 (2003); Grillaud et al., Arch of Pediatrics and Adolescent Medicine 12:1180-1186 (2005)).
Commercially, xylitol may be produced by chemical reduction of xylose, although this can present difficulties associated with separation and purification of xylose or xylitol from hydrolysates. Microbial systems for the production of xylitol have been described (Sirisansaneeyakul et al., J. Ferment. Bioeng. 80:565-570 (1995); Onishi et al., Agric. Biol. Chem. 30:1139-1144 (1966); Barbosa et al., J Ind. Microbiol. 3:241-251 (1988); Gong et al., Biotechnol. Lett. 3:125-130 (1981); Vandeska et al., World J. Microbiol. Biotechnol. 11:213-218 (1995); Dahiya et al., Cabdirect.org 292-303 (1990); Gong et al., Biotechnol. Bioeng. 25:85-102 (1983)). For example, yeast from the genus Candida has been described as being useful for xylitol production. However, Candida spp. may be opportunistic pathogens, so the use of these organisms in processes related to food products are not desirable.
The Metschnikowia species, methods and compositions provided herein meet these needs and provide other related advantages.